[Bug 582585] Re: getaddrinfo() returns duplicate addresses under AI_ADDRCONFIG

Tue Jan 29 01:40:24 UTC 2019

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------------------------------------------------------------------------
On 2012-12-17T17:08:20+00:00 Psimerda wrote:

getaddrinfo() with AI_ADDRCONFIG replaces all ::1 with 127.0.0.1 on
hosts without non-loopback IPv6 addresses. See the following test
result:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether f0:de:f1:b8:6a:ee brd ff:ff:ff:ff:ff:ff
    inet 84.246.161.88/28 brd 84.246.161.95 scope global eth0

getaddrinfo host="None" hints.ai_flags=AI_ADDRCONFIG:
  ::1
  127.0.0.1
getaddrinfo host="localhost" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
  127.0.0.1
getaddrinfo host="127.0.0.1" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
getaddrinfo host="localhost4" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
getaddrinfo host="::1" hints.ai_flags=AI_ADDRCONFIG:
  ::1
getaddrinfo host="localhost6" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
getaddrinfo host="195.47.235.3" hints.ai_flags=AI_ADDRCONFIG:
  195.47.235.3
getaddrinfo host="2a02:38::1001" hints.ai_flags=AI_ADDRCONFIG:
  2a02:38::1001
getaddrinfo host="info.nix.cz" hints.ai_flags=AI_ADDRCONFIG:
  195.47.235.3
getaddrinfo host="www.google.com" hints.ai_flags=AI_ADDRCONFIG:
  173.194.39.81
  173.194.39.82
  173.194.39.80
  173.194.39.84
  173.194.39.83

Especially notable are:

getaddrinfo(localhost) -> 127.0.0.1, 127.0.0.1 (duplicate)
getaddrinfo(localhost6) -> 127.0.0.1 (wrong)

Contents of /etc/hosts:

127.0.0.1	localhost localhost4
::1		localhost localhost6

Looks like some sort of black magic someone was trying to solve
something.

Reply at:
https://bugs.launchpad.net/ubuntu/+source/eglibc/+bug/582585/comments/2

------------------------------------------------------------------------
On 2012-12-17T17:09:23+00:00 Psimerda wrote:

Testing script:

#!/usr/bin/python3
import sys
from socket import *
hosts = [
    None,
    "localhost",
    "127.0.0.1",
    "localhost4",
    "::1",
    "localhost6",
    "195.47.235.3",
    "2a02:38::1001",
    "info.nix.cz",
    "www.google.com",
]
for host in hosts:
    print("getaddrinfo host=\"{}\" hints.ai_flags=AI_ADDRCONFIG:".format(host))
    try:
        for item in getaddrinfo(host, "http", AF_UNSPEC, SOCK_STREAM, SOL_TCP, AI_ADDRCONFIG):
            print("  {}".format(item[4][0]))
    except gaierror as error:
    	print("  !! {} !!".format(error))

Reply at:
https://bugs.launchpad.net/ubuntu/+source/eglibc/+bug/582585/comments/3

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https://bugs.launchpad.net/bugs/582585

Title:
  getaddrinfo() returns duplicate addresses under AI_ADDRCONFIG

Status in eglibc:
  Confirmed
Status in eglibc package in Ubuntu:
  Confirmed

Bug description:
  Presume I have a computer that has no global IPv6 addresses, but a few
  IPv4 addresses.

  Applications using getaddrinfo() with hints.ai_flags = AI_ADDRCONFIG
  set will properly omit IPv6 addresses, HOWEVER they will return
  duplicate IPv4 addresses.

  Demonstration code attached.

  Without IPv6 addresses:

  # show setup
  $ grep -w localhost /etc/hosts
  127.0.0.1	localhost
  ::1     localhost ip6-localhost ip6-loopback
  $ ip a s | grep inet
      inet 127.0.0.1/8 scope host lo
      inet6 ::1/128 scope host 
      inet 192.168.0.4/24 brd 192.168.0.255 scope global eth0
      inet6 fe80::226:XXXX:XXXX:XXXX/64 scope link  # masked for privacy

  # compile test case
  $ gcc -Wall -Wextra -pedantic -O -o libcbug-demo libcbug-demo.c

  # run test case
  $ ./libcbug-demo localhost echo
  Address 1: 127.0.0.1
  Address 2: 127.0.0.1

  (127.0.0.1 should be listed only once, Solaris 10 for instance
  achieves that)

  Now configure a fake IPv6 address (don't do this on hosts with real
  IPv6 connectivity, it suffices to use your real IPv6 address) and re-
  run the application:

  $ ip a a 2001::2001 dev eth0 # set up IPv6
  $ ./libcbug-demo localhost echo
  Address 1: ::1
  Address 2: 127.0.0.1
  $ ip a d 2001::2001 dev eth0 # deconfigure bogus address

  (This is fine)

  Practical consequence: excessive connection retries by applications
  that possibly take a long time.

  This isn't Ubuntu specific.

  ProblemType: Bug
  DistroRelease: Ubuntu 10.04
  Package: libc6 2.11.1-0ubuntu7
  ProcVersionSignature: Ubuntu 2.6.32-22.33-generic 2.6.32.11+drm33.2
  Uname: Linux 2.6.32-22-generic x86_64
  NonfreeKernelModules: fglrx
  Architecture: amd64
  Date: Wed May 19 01:13:51 2010
  ProcEnviron:
   PATH=(custom, no user)
   LANG=de_DE.UTF-8
   SHELL=/bin/bash
  SourcePackage: eglibc

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